78 GS5/650 street/track motor

[Guest]

For the past few months i have been doing research and collecting parts, for this winters build, The idea in mind is a road legal track bike to run at a vintage track day at Watkins Glen next year, Honestly i dont really expect to be competitive this is simple an effort to prove something to myself, with that said, here is the current plan and list of parts; using the crankcase ect. form my 78 550GS(I must have a kickstart) we will swap the block and head with one from a 81 650GS, I am leaning toward using the 650 cams with the idea it will have some street drive-ability, but i do not know if this will have an effect on high RPMs? I have a Dynatek 2k ignition system (and programing software) instead of points to keep ignition constant through High RPMs, I do not know what coils to use, and was wondering about these iridium 4 electrode plugs my buddy mentioned. I was also thinking of having the head machined to increase compression, I am told this will result in more heat being produced, so i think a compufire R/R and an oil cooler may reduce the heat?

This entire build is a learning process, I am b y no means a pro

[rapidray]

Rob, call me at 714--356-7845. Ray.

[trippivot]

road legal track bike

ok I like the ambition of your post.

You have such focus on your engine. GREAT! I like 1 of a kind !

Not knowing what your budget is planned at, and I may be jumping the gun offering advice. I hope you don't mind, but some of that crap on your list will not get you through a corner. Tons of money will solve any problem- do you want to sink $2000. into the engine and not ride it around a corner fast?

I believe 3% suspension improvement is equal to 10% more power.

. A Fact is, dollar for dollar one gets more riding improvement from suspension upgrades.

The best tires money can buy/rules allow, perfect balance on the wheels is a great start. Then good performance rear shocks, maybe some blueprinting on the inner dampening rods along with stiffer springs for the feel. Shaving off every ounce of non essential weight.

mods like that will allow you to ride faster in better control with less power. (less money too)

just a dyna "S", green 3 ohm coils,dyna wires, and regular NGK plugs is all you need for ignition. not going to need an oil cooler. cams are a cinch. Forged pistons will handle 8K~10K RPM's don't run stock cast ones just cause pops yoshi did. APE tool steel wrist pins are very important.

when you mill the head and you have to modify the valve pockets in the piston crowns..

you wrote a lot-a- bucks out of your pocket by wanting a exotic engine instead of concentrating on your final goal --a good riding toy.

post pictures, I'm interested in 1 of a kind anything.

[Suzuki_Don]

I would go with 550 cams if I was you. They are more peaky than the 650 cams and will produce more power above 5k. The 650 cams give great torque, but that's not what you want. You want power at high revs.

[rapidray]

If you are building a TRACK engine, you want RACE parts, not stock. You want parts that are stronger & will make power, not parts that are over 30 years old & have who knows how much abuse on them already. Ray.

[hampshirehog]

I wouldn't go spending a fortune on bits for the motor. Those little engines are unburstable and will happily rev waaay in to the redline making good power. Concentrate on setting the thing up right. Like Tripivot says spend on the suspension, plus, I would add, spend on the brakes and tyres and dump as much weight as you can - the 550 is a heavy bike.

[dansofield550]

building a 550 with a top end from 650 now , i measured the 650 and 550 cam and found no difference , so kept the 650 one in the 650 head as they'll be bedded into the journals right , only thing i need to do was change the cam chain wheels over from 550 onto the 650 cam and the 650's are bigger and would of course mess up the cam timing,



the 550 cam chain wheels needed to be drilled out at the 650 has bigger bolts .

porting the head will help a lot too, mine had real large steps in the inlet's , smoothed those out easy enough .
, had to nibble some metal from the upper crank case where the barrels fit as there are casting lumps and marks that will stop it going on ,

, its all an easy way to make half as much power again than the stock 550, on standard suspension and weight i've no idea what it'll be like but mines not standard

[Suzuki_Don]

i measured the 650 and 550 cam and found no difference ,

Not true. Incorrect.

The 550 cam has 260 degrees duration and 7.08mm lift on both camshafts (intake and exhaust).

The 650 only has 252 degrees duration and has 7.53mm lift on the exhaust and 8.12mm lift on the intake.

Hope this helps.

[dansofield550]

dont think i was clean in what i meant, namely the journals are the same on 550 as the journals on 650 , so kept the cams as they're bedded in to the head after god know how long spinning around , the 550 was worn a lot too.

interesting about the different profiles i didn't bother checking those against each other , what do you suppose the difference would be if i did fit 550 cams in a 650 head?

[Buffalo Bill]

Are you a rider or an engineer?

Really, your main interest is building an engine the hard way.
A rider is a jockey, that's what he wants to do, so that's what he does best.

I think it's gonna take you, one year to build it, one year tune it, one year to build the bike, one year to tune it, enough to finish two track days in a row.

Pops Yoshimura was not a rider, he was a master craftsman, tuner and fabricator.

Fine engineering project, but all that is not riding track days.

If you want to be on the track and learning how to ride next summer, you better choose a 650-750, or a 1000.
Just preparing one of those will take you all winter.

Bill

[GregT]

Many a true word posted....Bill's quite right. If your main interest is getting out there and riding buy something more track appropriate.

The sheer amount of work required is why I'm flat out building race bikes for customers....and not racing myself.

Cams...go with the 650 cams. For your level of experience,a wide smooth powerband will suit better. The 550 cams will bias the power characteristics more towards the top end of the rev range.

[dansofield550]

apologies for hijacking the thread a little , but what you (greg t) recommend to do with the cam chain tensioner ? a fixed type or stick to standard

[hampshirehog]

Bill's not necessarily right. For a start, if you're learning to race then a 250 is a good starter. It'll teach you about braking, using the powerband, picking the quickest line etc much more than you'll learn on a bigger bike. If you lose 5 mph on a 250 'cos you got something wrong it's a massive loss.

Plus it all depends how competitive you want to be. If you want to win you had better have deep pockets. Sh*t, even MZ racing over here needs an awful lot of £s a year to be a front runner.

And you can forget all about winning if you weigh 13 stone. I'll always maintain I was a better rider than my old mate Cliff when we had a pop on the circuit back in the early 80s and I don't think he'd argue (well, we did enough of that then....). Only he was 5'8" and under 10 stone, I was 6'1" and over 13 stone so he rode and I waited around with the spanners and drove the van.

[Suzuki_Don]

Many a true word posted....Bill's quite right. If your main interest is getting out there and riding buy something more track appropriate.

The sheer amount of work required is why I'm flat out building race bikes for customers....and not racing myself.

Cams...go with the 650 cams. For your level of experience,a wide smooth powerband will suit better. The 550 cams will bias the power characteristics more towards the top end of the rev range.

In my experience the 550 cams have precious little below 3k, come on harder at 5k and really take off at 7k. Where as the 650 cams have a smoother transition throughout the rev range but the torque always makes sure your moving quite quickly. For instance on my bike the motor will pull in 6th from 25mph to over 125mph without any hesitation or grumbling. In the lower gears it is even quicker.

Sorry I misunderstood you earlier. I thought you were talking about taking lobe measurements.

BTW it is only an afternoons work to swap the cams so why not try the 550s and get a feel for what they feel like performance wise and then swap to the 650 cams and do likewise. There is nothing like "seat of the pants" monitoring to see which has the best performance for your needs.

[GregT]

apologies for hijacking the thread a little , but what you (greg t) recommend to do with the cam chain tensioner ? a fixed type or stick to standard

If you're serious about revving the thing, manual tensioner every time.

The HampshireHog is also correct but out here we've got a very good Junior roadracing scene and it's amusing to watch the juniors when they're put on something like an old GS.
They've learned on modern 150's and 250's and know the importance of maintaining corner speed and momentum....try that on a flexible old GS on skinny tires.....with brakes that are non existent by modern standards.
If you're an older chap wanting to have a quiet go on track the GS will suit - but it's not the starting point for a career.